Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA297

Poster Communications

Quantification of information transfer via gonadotropin-releasing hormone receptors (GnRHR) reveals a marked loss of information through signalling

H. Alobaid1, M. voliotis2,3, K. Tsaneva-Atanasova2,3, C. McArdle1

1. Bristol Medical School, University of Bristol, Bristol, United Kingdom. 2. EPSRC Centre for Predictive Modeling in Healthcare, University of Exeter, Exeter, United Kingdom. 3. Department of Mathematics and Living Systems Institute, College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, United Kingdom.

Gonadotropin-releasing hormone (GnRH) is a hypothalamic neuropeptide that acts via GnRHR on the pituitary gonadotrope. It is secreted in pulses and acts via GnRHR to activate ERK and Nuclear Factor of Activated T-cells (NFAT). Both of which mediate GnRH effects on the synthesis of reproductive hormones. Using automated fluorescence microscopy, effects of GnRH on cell signalling in individual cells can be quantified revealing marked cell-cell heterogeneity. Information theoretic approaches, which consider cell-cell heterogeneity and its impact on information transfer, can be used to quantify information transfer via cell signalling pathways. Here we use the mutual information (MI) between GnRH concentration and measured responses (I(response; GnRH)) as a measure of information transfer via GnRHR. MI is measured in Bits, with an MI of 1 Bit indicating a system that can unambiguously distinguish between two inputs. Initially, we did this in fixed LbT2 cells (gonadotrope-derived cells). The cells were stimulated with various concentrations of GnRH (0-10-6M) before staining for ppERK (immunohistochemistry), and in some experiments, cells were infected with recombinant adenovirus for expression of NFAT- EFP. As Ca2+ causes NFAT to translocate to the nucleus, the nuclear fraction (NF) provides a readout for elevation of the cytoplasmic Ca2+ concentration ([Ca2+]i) by GnRH. Our data, therefore, suggest that most information from the environment is lost through signalling. The I(ppERK; GnRH) and I(NFAT-NF; GnRH) values were always <1Bit despite 3Bit input. Joint sensing of ppERK and NFAT-NF increased slightly MI values [1,2], suggesting that, by ignoring response dynamics, information transfer is underestimated. Therefore, using live cell measurements and MI calculations taking response trajectory into account, NFAT-EFP translocation was tracked in response to a single pulse of GnRH. The I(NFAT-NF; GnRH) values were ~0.5 Bit at 30 min and remained elevated for 60 min. Taking response trajectories into account increased MI values to ~0.65 Bit. We also tracked NFAT-EFP translocation responses in cells receiving two pulses of GnRH and found that the information gain from the second pulse was small. Similar experiments were performed using Fluo-4 measurements of [Ca2+]i. The I(Ca2+; GnRH) values were ~0.8 Bit, 24sec after stimulation, reducing to ~0.66 Bit after 2 min. These values were increased to 1Bit by consideration of trajectories. Thus, LbT2 cells are unreliable sensors of GnRH concentration because a considerable amount of information is lost through signalling. Although joint sensing, trajectory sensing and sensing repeated pulses increased information transfer, this was typically <20% suggesting that most information is lost early in the GnRH signalling cascade, prior to Ca2+ mobilisation.

Where applicable, experiments conform with Society ethical requirements